The present invention relates to a method of detecting an edge bead removal line (EBR line) on a wafer.
In semiconductor manufacture wafers are sequentially processed during the manufacturing process in a multitude of processing steps, wherein a plurality of similar, repetitive structural elements, the so-called dies, are produced on a wafer. As the integration density increases, the quality of the structures formed on the wafer is subject to increasing demands. To be able to verify the quality of the structures formed and to find defects, if any, the requirements as to the quality, the precision and the reproducibility of the components and process steps for handling the wafer are correspondingly stringent.
During the manufacturing process, photoresist layers are usually applied in the so-called spinning process, wherein the photo resist is applied near or in the center of the wafer and is spread by rotating the wafer on its surface. This process results in photoresist collecting on the edge of the wafer, the so called edge beads, which are many times thicker than the remaining photoresist layer. In order to avoid negatively affecting the manufacturing process in its subsequent processing steps and the function of the integrated circuits (ICs) to be manufactured, these edge beads have to be removed. To this end, however, they have to be reliably detected. This is why the removal of the edge beads comes to be integrated as a standard process during the manufacturing of wafers.
A method for removing and for better detecting the edge beads is disclosed for example in US2004/0223141 A1. In this document it is suggested that the contrast between the silicon layer of the wafer and an applied photoresist layer be improved by using a special illumination. To do this, the wafer has to be lighted separately with s and p polarized light in the vicinity of the Brewster angle of silicon or the photoresist layer. Subsequently the difference between the images of the reflected s polarized radiation and the image of the reflected p polarized radiation is evaluated to improve the contrast.
Since usually structures from previous processing steps are already present on the wafer, a plurality of lines or edges will be detected in the resulting gray scale image using the prior art methods. However, these may not always be easy to unequivocally associate with their cause. In particular, it is not possible to identify a certain line or edge as an edge bead removal line in an unequivocal manner.